Method for circuits inspection and method of the same

ABSTRACT

A method for circuit inspection comprises steps of providing a substrate having a conductive line; and forming a metal layer on at least the conductive layer to increase a contrast between the conductive layer and adjacent area for the circuit inspection. The method further comprising removing the metal layer. The metal layer is removed by a mixture of nitric acid, hydrogen peroxide and fluoride boric acid. The metal includes Silver, Nickel or Tin. The deposit metal can be removed by inter diffusion and form intermetallic compounds (for example Cu 6 Sn 5 ) into the under laying conducting line.

TECHNICAL FIELD

The present invention relates to a method for circuit inspection, andmore particularly relates to a method for circuit inspection byincreasing the contrast between developing and no developing area.

BACKGROUND OF THE INVENTION

Optical inspection (AOI) systems are used for inspecting the defects ofcircuit; the system can be used for inspecting proper component presenceand orientation, proper solder joint formation, conducting line andunwanted residue, for example photo resist residue.

As the line width of a circuit is getting narrower, it is getting easierto make mistake when doing inspection by human eye. Traditionally, tofind the defect of a circuit need the experience accumulated andapplying cause and effect Diagram to find out the problem; it is notonly time consuming and also hard to find qualified personnel to do thejob. Therefore, automated optical inspection has become popular forcircuit inspection technique is the past few years.

The main automated inspection methods include inspecting by white lightand by laser beams. The inspection method by white light is projectingwhite light on the circuit and then sensing the reflecting light signalby light sensor; at last the receiving signal is treated by the imageprocessing software for defect identification. Another method isprojecting laser beam to excite the organic fluorescence material of nonmetallic part and then receiving laser induced fluorescence by lightsensor. By predetermined value, the metal part and non metal part of thereceiving grey-scale image can be resolved; therefore the image can beused for defect inspection.

Most of the invention relates to automated optical inspection isendeavor in developing different lighting modes, signal detecting modesor other simulated methods. For example, U.S. Pat. No. 7,075,565discloses an automated optical inspection system includes a plurality ofasynchronously cameras for providing image data of a printed circuitboard. The circuit board is divided into fields of view that are to beimaged in one or more cameras in one or more lighting modes. The systemallows the full bandwidth of the cameras to be utilized for reducing theinspection time of the board. Taiwan Patent No. I244359 discloses amethod for inspection the defect of a printed circuit board byestablishing standard component templates in advance and then take thesetemplates for defect inspection. Taiwan Patent No. I258583 discloses alighting system for generating light with high and uniform luminescencein a small area to enhance the image resolution.

From the prior art, referring to FIG. 1, the contrast of the developmentand un-development area is very low. The user can not distinguish thedeveloped area from each other. Therefore, it is unlikely to inspect theresult by the operator.

Therefore, the present invention provides a method for circuitinspection, more particularly relates to a method for circuit inspectionby increasing the contrast between developing and no developing area;the present method can provide a circuit image with enhanced contrast toovercome the shortcomings of prior arts.

SUMMARY OF THE INVENTION

The present invention relates to a method by enhancing the contrast ofdeveloped and undeveloped areas. The present method utilizing a chemicaldeposit on the conducting line to achieves the goal of presentinvention. Besides enhancing the contrast, the chemical can also act asconducting media; therefore, if the stripping step can't totally removethe chemical, the residue can also act as part of conducting line andwould not raise the performance issue.

A method for IC inspection comprises providing a substrate having aconductive line; and forming a metal layer on at least the conductivelayer to increase a contrast between the conductive layer and adjacentarea for the IC inspection. The method further comprising removing themetal layer. The metal layer is removed by a mixture of nitric acid,hydrogen peroxide and fluoride boric acid. The metal includes Silver,Nickel or Tin. The deposit metal can be removed by inter diffusion andform intermetallic compound (for example Cu₆Sn₅ if the under layingconducting line is copper) into the under laying conducting line.

Alternatively, the method for circuit inspection comprises a step ofproviding a substrate having a conductive line; and forming a metallayer on at least the conductive layer to increase a contrast betweenthe developed area and un-developed area for the circuit inspection. Themethod further comprises removing the metal layer. The metal layer isremoved by a mixture of nitric acid, hydrogen peroxide and fluorideboric acid. The metal includes Silver, Nickel or Tin. The deposit metalcan be removed by inter diffusion and form intermetallic compound (forexample Cu₆Sn₅) into the under laying conducting line.

A method for residual photoresist inspection comprises a step ofproviding a substrate having an inspection area; and forming a metallayer on at least the substrate to increase a contrast between theresidual photoresist and adjacent area for inspection.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, and other features and advantages of the presentinvention will become more apparent after reading the following detaileddescription when taken in conjunction with the drawings, in which:

FIG. 1 is a schematic diagram of the inspection method according to thepresent invention.

FIG. 2 is a schematic diagram of the inspection method according to thepresent invention.

FIG. 3 is a schematic diagram of the result of the inspection methodaccording to the present invention.

FIG. 4 is a schematic diagram of the result of the inspection methodaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Some sample embodiments of the invention will now be described ingreater detail. Nevertheless, it should be recognized that the presentinvention can be practiced in a wide range of other embodiments besidesthose explicitly described, and the scope of the present invention isexpressly not limited except as specified in the accompanying claims.Then, the components of the different elements are not shown to scale.Some dimensions of the related components are exaggerated andmeaningless portions are not drawn to provide clearer description andcomprehension of the present invention.

The present invention relates to a method for enhancing the contrast ofa developed and un-developed areas. The present invention includes astep of forming a metal on a conductive line to increase the contrastbetween the conductive line and other area. The metal could be ImmersionTin, Immersion Silver or Electroless Nickel. Take Tin as an example,referring to FIG. 2, Tin is deposited on a conducting line, for examplemade of copper (Cu) to increase the contrast. A layer of intermetalliccompound Cu₆Sn₅ forms between the Cu and Sn layers due to the materialssolid-state diffusion. FIG. 2 also illustrates heating time versusthickness of intermetallic layer, as the controlled maximum depositionthickness of Sn is 0.6 μm, the thickness of intermetallic layer isincreased with heating time and the thickness stabilized after 4 hours.Optionally, after finishing inspection, Sn deposition can be stripped bychemical reaction, for example, utilizing the mixture of nitric acid,hydrogen peroxide and fluoride boric acid for stripping the Sndeposition. On the contrary, this layer can be remained on theconductive layer.

FIG. 3 illustrates the OM inspection picture before and after Sndeposits on the inspection area. The upper portion is the cross-sectionand top views, and the pictures are the top views of the inspectionarea. We can easily identify that after immersed Sn deposits on theinspection area, the contrast is enhanced from the illustration.

Because Sn fails to deposit on top of the photo resist, therefore theimmersion Sn can also be utilized for find out the unwanted residualphoto resist. FIG. 4 is another OM inspection picture before and afterSn deposits on the inspection area. Left side is the original method,the contrast is very low, and the right side is the present invention.After immersion Sn is formed, it is observed that Sn would not depositon the residual photo resist and the unwanted photo resist residual canbe easily identified.

Although specific embodiments have been illustrated and described, itwill be obvious to those skilled in the art that various modificationsmay be made without departing from what is intended to be limited solelyby the appended claims.

1. A method for circuit inspection, comprising: providing a substratehaving a conductive line and a photoresist layer; after the photoresistlayer is formed and before the photoresist layer is removed, forming acontrast metal layer on at least said conductive line without formingthe contrast metal layer on top of the photoresist layer to increase acontrast betwcen said conductive line and adjacent area for said circuitinspection.
 2. The method in claim 1, further comprising removing saidcontrast metal layer.
 3. The method in claim 2, wherein said contrastmetal layer is removed by a mixture of nitric acid, hydrogen peroxideand fluoride boric acid.
 4. The method in claim 1, wherein said contrastmetal layer includes Silver, Nickel or Tin.
 5. The method in claim 1,wherein said contrast metal layer is removed by inter diffusion to forman intermetallic compound into said conductive line.
 6. A method forcircuit inspection, comprising: providing a substrate having aconductive line and a photoresist layer; after the photoresist layer isformed and before the photoresist layer is removed, forming a contrastmetal layer on at least said conductive line without forming thecontrast metal layer on top of the photoresist layer to increase acontrast between development area and un-development area for saidcircuit inspection.
 7. The method in claim 6, further comprisingremoving said contrast metal layer.
 8. The method in claim 7, whereinsaid contrast metal layer is removed by a mixture of nitric acid,hydrogen peroxide and fluoride boric acid.
 9. The method in claim 6,wherein said contrast metal layer includes Silver, Nickel or Tin. 10.The method in claim 6, wherein said contrast metal layer is removed byinter diffusion to form an intermetallic compound into said conductiveline.
 11. A method for residual photoresist inspection, comprising:providing a substrate having an inspection area and a photoresist layer:after the photoresist layer is formed and before the photoresist layeris removed, forming a contrast metal layer on at least said substratewithout forming the contrast metal layer on top of the photoresist layerto increase a contrast bctween a residual photoresist and adjacent areafor inspection.
 12. The method in claim 11, fwTher comprising removingsaid contrast metal layer.
 13. The method in claim 12, wherein saidcontrast metal layer is removed by a mixture of nitric acid, hydrogenperoxide and fluoride boric acid.
 14. The method in claim 11, whereinsaid contrast metal includes Silver, Nickel or Tin.
 15. The method inclaim 11, wherein said contrast metal layer is removed by interdiffusion and form intermetallic compound into said conductive line.